The present invention relates generally to a liquid-atomizing or other spray nozzle, and more particularly to a dual orifice fuel nozzle having an internal mixing chamber for delivering an aqueous fuel emulsion providing NO.sub.x emission control.
Liquid atomizing nozzles are employed, for example, in gas turbine combustion engines and the like for delivering a metered amount of fuel from a manifold into a combustion chamber of the engine as an atomized spray of droplets for mixing with combustion air. Typically, the fuel is supplied at a relatively high pressure from the manifold into an internal swirl chamber of the nozzle which imparts a generally helical vector component to the fuel flow. The fuel flow exits the swirl chamber through a discharge orifice of the nozzle as a thin, conical vortex of fuel surrounding a central core of air. As the vortex advances away from the discharge orifice, it is separated into a conical spray of droplets. To improve the atomization of the fuel for increased combustion efficiency, the flow through the nozzle may be assisted with a stream of high velocity and/or high pressure air. For some applications, a pair of nozzles are used in combination for increasing the fuel throughput rate or for delivering a second fluid such as water for intermixing with the fuel and combustion air.
In basic construction, fuel nozzle assemblies of the type herein involved are constructed as having an inlet fitting which is configured for attachment to the manifold of the engine, and a nozzle or tip which is disposed within the combustion chamber of the engine as having one or more discharge orifices for atomizing the fuel. A generally tubular stem or strut is provided to extend in fluid communication between the nozzle and the fitting for supporting the nozzle relative to the manifold. The stem may include one or more internal fuel conduits for suppling fuel to one or more spray orifices defined within the nozzle. A flange may be formed integrally with the stem as including a plurality of apertures for the mounting of the nozzle to the wall of the combustion chamber. Appropriate check valves and flow dividers may be incorporated within the nozzle or stem for regulating the flow of fuel through the nozzle. A heat shield assembly such as a metal sleeve, shroud, or the like additionally is included to surround the portion of the stem which is disposed within the engine casing. The shield provides a thermal barrier which insulates the fuel from carbonization or "choking," the products of which are known to accumulate within the orifices and fuels passages of the nozzle and stem resulting in the restriction of the flow of fuel therethrough.
Fuel nozzles are designed to provide optimum fuel atomization and flow characteristics under the various operating conditions of the engine. Conventional nozzle types include simplex or single orifice, duplex or dual orifice, and variable port designs of varying complexity and performance. Representative nozzles of these types are disclosed, for example, in U.S. Pat. Nos. 3,013,732; 3,159,971; 3,912,164; 4,134,606; 4,258,544; 4,613,079; 4,735,044; 5,174,504; 5,269,468; 5,423,178; and 5,435,884.
With respect to nozzles of the noted dual orifice variety, such nozzles are constructed, as is illustrated in U.S. Pat. No. 5,423,178, of a pair of coaxially-disposed, generally-tubular body members which define primary and secondary fuel passages. The primary fuel passages extends to a primary discharge orifice of the nozzle via a swirl chamber, plug, slots, or the like for developing a generally helical flow pattern. The secondary fuel passage, in turn, extends to a secondary, usually annular, discharge orifice disposed radially concentrically about the central primary orifice. A flow divider may be provided to direct fuel flow through only the primary orifice for efficient atomization at low throughput rates for discharged, and through both the primary and secondary orifices for higher throughput rates.
As described, the primary and secondary orifices of dual orifice nozzles typically are utilized to provide a frusto-conical atomization profile which may be characterized as including a narrower, interior fuel cone from the primary orifice and a wider, exterior fuel cone from the secondary orifice. Proposals have been made, however, for additionally utilizing the primary or secondary orifice nozzles for injecting water into the combustion chamber.
In this regard, designers of fuel nozzles are confronted by the dual requirements of lower allowable combustion exhaust emission prescribed by government regulations and high combustion efficiency required by industry. It is known that the admixing of water with the fuel provides a quench that limits the maximum combustion temperature which, in turn, is effective in reducing emissions of nitrous oxides (NO.sub.x) in the exhaust gas effluent. Water injection additionally is used for smoke reduction, to minimize carbon formation, i.e., coking, and for thrust augmentation. Conventional nozzle arrangements comprehend the use of external equipment to deliver a pre-emulsified stream of fuel and water to the nozzle, or the delivering of the water from the nozzle as a separate flow stream which is injected from a position located radially outward of the fuel flow stream.
For example, U.S. Pat. No. 4,600,151 discloses a representative fuel injector assembly for a gas turbine engine having water injection capability. The assembly includes an annular shroud within which are received a plurality of concentric sleeves. The sleeves are disposed in a spaced-apart relation to define an outer fuel receiving chamber, an intermediate water or auxiliary fuel receiving chamber, and an inner air-receiving chamber.
U.S. Pat. Nos. 4,701,124 and 5,062,792 disclose another representative fuel nozzle assembly for a gas turbine engine having water injection capability. The assembly includes a pilot burner which is located near an end of a flame tube for generating a pilot flame. A central tube provides fuel to the pilot burner, with water or steam being provided to the fuel via a pair of radially-disposed injection nozzles.
U.S. Pat. No. 5,228,283 discloses another fuel nozzle assembly for reduced NO.sub.x emissions. The assembly includes an elongate water delivery pipe having an interior passageway extending from a rearward end to a forward open end. A mounting coupling is affixed to the exterior of the rearward end of the pipe for its mounting within a rearward end of a fuel nozzle body. The forward end of the pipe is provided with an interior water swirler and an exterior fuel swirler, with the forward end of the fuel nozzle body being provided with an air swirler. Such an arrangement provides an outer conical air spray, an intermediate fuel spray, and an inner conical water spray at the fuel nozzle tip.
U.S. Pat. No. 3,638,865 discloses another dual orifice fuel nozzle for a gas trubine engine. The nozzle includes a shrouded and shielded discharge head. The discharge head is constructed as having an annular orifice and a frusto-conical guide surface. The shroud and the shield define a generally axially-extending passageway which is disposed radially about the head.
U.S. Pat. No. 3,685,741 discloses another dual orifice fuel nozzle for a gas trubine engine. The nozzle includes a primary nozzle body which is disposed between a secondary nozzle body and a housing. The nozzle bodies define primary and secondary fuel passages leading, respectively, to primary and second swirl chambers and discharge orifices. The secondary fuel passage is located centrally of the nozzle tip end, with the primary passage being disposed radially outwardly from the secondary passage.
U.S. Pat. No. 3,013,732 discloses another dual orifice fuel nozzle for a gas turbine engine. Primary and secondary fuel passages are employed to convey fuel through primary and secondary discharge orifices via, respectively, a swirl plug and swirl slots.
U.S. Pat. No. 4,854,127 discloses an air swirler and fuel injector for a gas turbine combustion engine. A primary fuel flow is supplied into a primary combustion zone by an inner annulus of swirling air. A secondary fuel flow is supplied into a a secondary combustion zone by an outer annulus of air for combustion at higher fuel flow rates. The secondary fuel flow may be separately injected into the outer annulus via a conduit, or combined with the primary fuel in the injector body.
As aforementioned, methodologies for providing NO.sub.x emmision control heretofore have involved the use of external mixing equipment or conventional dual orifice nozzle arrangements. It has been observed, however, that imperfect mixing of the water and fuel components produces concentrations in the combustion zone of water poor and water rich domains. Within the water poor domains are developed temperature localizations which are higher than than optimum for controlling NO.sub.x emission. Likewise, within the water rich domains are developed temperature localizations which are lower than optimum for efficient combustion minimzing hydrocarbon and carbon monoxide generation. Accordingly, it will be appreciated that improvements in the design of fuel nozzles for water injection would be well-received by industry. A preferred design would ensure uniform mixing of the water and fuel components without the need and expense of external mixing equipment.